An international research team has demonstrated a new approach to 4D-printed shape-morphing implants that opens the door to increasingly personalised healthcare.

The findings, outlined in the journal Additive Manufacturing, highlight how material degradation can be used to trigger controlled shape change of implanted material.

Specifically, researchers studied the mechanical, biological and degradation behaviour of polyvinyl alcohol (PVA) and polyethylene terephthalate glycol-modified (PETG) to engineer multi-material 4D printed actuators, and whose movement was activated over time by exposure to water.

They showed that the resulting gradual PVA degradation can serve as a reliable, predictable stimulus to initiate shape morphing, while PETG serves as a structural component that stores and releases elastic energy.

“This strategy introduces degradation as a powerful, yet underexplored, mechanism for triggering actuation in 4D-printed systems,” explains Dr. William Solórzano, one of the authors behind the publication.

Researchers used Fused Filament Fabrication (FFF) to combine PVA and PETG, creating multi-material devices in which the PVA serves as a temporary mechanical constraint. As it erodes over time, its mechanical integrity is reduced, allowing the internal energy stored in the PETG to be released.

“This controlled release of elastic energy drives a programmed shape transformation over time”, says Dr. Solórzano.

This represents a novel approach to inducing a slow shape change response in 4D-printed materials, which typically rely on rapid triggering stimuli such as temperature, light, electric fields or humidity.

Their capacity for controlled geometric transformations makes them particularly promising for applications such as implantable medical devices, tissue engineering scaffolds and drug delivery systems, where delayed or gradual actuation can be critical.

Despite its importance for long-term and biomedical uses, degradation-induced actuation remains largely unexplored in this field. Exploring degradation as a triggering mechanism in 4D-printed devices opens up significant possibilities in diverse fields where a defined response over longer periods of time can be advantageous. For example, medical applications where healing and growth processes require sufficient healing time.

The recent study is the work of researchers Prof. Andrés Díaz Lantada and Dr. Solórzano from the Technical University of Madrid, Drs. Jennifer Patterson, Pedro J. Díaz Payno and Vanesa Martínez from IMDEA Materials Institute, and Dr. Alexander Kopp from German medical technology manufacturer Meotec, as part of the European BIOMET4D project.

It highlights how PVA transitions from brittle to more ductile behaviour as it degrades in water, accompanied by reductions in stiffness, strength and molecular weight. PETG, by contrast, remains mechanically robust under immersion and effectively stores and releases elastic energy, making it well suited for controlled actuation in aqueous environments.

This principle was further demonstrated in a 4D shock absorber, highlighting the feasibility of degradation-triggered mechanical responses.

Beyond mechanical performance, the study also assessed the biological response of both materials. Cytotoxicity tests confirmed that PVA dissolves rapidly without harmful effects, while PETG remains highly cytocompatible, reinforcing the suitability of both polymers for biomedical use.

“By combining PETG’s flexibility and energy storage capacity with PVA’s programmable degradability, the study presents a cost-effective, scalable and versatile strategy for prototyping advanced 4D actuators,” says fellow author Dr. Patterson, coordinator of BIOMET4D.

“Some examples of where this can be put into practice are in the treatment of craniosynostosis, as well as in skin expansion treatments, the two use cases of the BIOMET4D project.”

“These actuators enable time-dependent transformations without the need for continuous external stimuli or complex activation systems, an approach which could also be extended to high-performance additive manufacturing processes and materials,” she concludes.

BIOMET4D has received funding from the EIC Pathfinder under grant agreement No 101047008. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Innovation Council and SMEs Executive Agency (EISMEA). Neither the European Union nor the EISMEA can be held responsible for them.